The present invention relates an apparatus and method for correcting the Z-height, gram load, pitch static attitude and/or the roll static attitude during assembly of a hard disk drive.
Magnetic recording hard disk drives are widely used in computers and data processing systems for storing information in digital form. These disk drives commonly include (i) a drive housing having a base and a pivot, (ii) one or more rotating storage disks, (iii) one or more actuator arms that are mounted on the pivot, and (iv) one or more head suspension assemblies. Each storage disk typically includes one or more tracks.
FIG. 1A illustrates a prior art head actuator assembly 10P including an actuator hub 12P, an actuator arm 14P, and a head suspension assembly 16P having a load beam 18P, a slider 20P, and a flexure 22P that secures the slider 20P to the load beam 18P. The slider 20P includes an air bearing surface 24P. The load beam 18P is bent at an angle xcex8. As is well known in the art, an additional head suspension assembly (not shown) is typically attached to the bottom surface of the actuator arm 14P. Further, the head actuator assembly 10P typically includes a plurality of actuator arms 14P, each having one or more head suspension assemblies 16P.
FIG. 1B illustrates the relationship of a prior art head suspension assembly 16P to a storage disk 26P when the storage disk 26P is not rotating. In this position, the head suspension assembly 16P is in a xe2x80x9cloadedxe2x80x9d state. In the loaded state, the load beam 18P is bent so that the angle xcex8 (illustrated in FIG. 1A) is reduced from the angle xcex8 illustrated in FIG. 1A and the angle xcex8 is typically greater than zero. Because the load beam 18P resists this deformation, a force, commonly referred to as the gram load, is transmitted to the slider 20P. The distance between the air bearing surface 24P of the slider 20P and a top mounting side 28P of the actuator arm 14P is commonly referred to as the Z height.
FIG. 1C illustrates a prior art view of the load beam 18P being held in the loaded state by a pin 30P. In this configuration, an angle xcex1 is defined by the air bearing surface 24P and the top surface 28P. The angle xcex1 is referred to as the pitch static attitude (PSA) of the slider 20P.
FIG. 1D illustrates a prior art end view of the head suspension assembly 16P with the load beam 18P held in the loaded state. An angle xcex2 is defined by the horizontal tilt of the air bearing surface 24P of the slider 20P relative to the top mounting side 28P of the actuator arm 14P. The angle xcex2 is referred to as the roll static attitude (RSA) of the slider 20P. The term xe2x80x9cstatic attitudexe2x80x9d is used to describe either the PSA or the RSA, or both parameters together. The load beam 18P and the flexure 22P are also illustrated in FIG. 1D.
FIG. 1E illustrates a prior art view of the relationship of the head suspension assembly 16P to the storage disk 26P when the storage disk 26P is rotating. The rotation of the storage disk 26P causes the slider 20P to ride on an air bearing a distance xe2x80x9chxe2x80x9d from the storage disk 26P. The distance xe2x80x9chxe2x80x9d is referred to as the xe2x80x9cflying heightxe2x80x9d of the slider 20P and represents the position that the slider 20P occupies when the storage disk 26P is rotating during normal operation of the disk drive. The load beam 18P and a portion of the actuator arm 14P are also illustrated in FIG. 1E.
The need for increased storage capacity, compact construction, and reduced cost has led to disk drives having fewer storage disks, with each storage disk having increased track density. As track density increases, it is necessary to decrease the flying height of the slider and have tighter control on the flying height. More specifically, if the flying height is not maintained within a certain range, the quality of the data transferred to and from the storage disk is degraded. As a result thereof, accurately controlling the flying height of the slider is critical to the accurate transfer and/or retrieval of information from the storage disk.
The flying height of the slider is influenced by a number of factors, including the rotation speed of the storage disk, the design of the air bearing surfaces of the slider, the pitch static attitude, the roll static attitude, the gram load, and the Z height. For example, the flying height is often higher than nominal if the Z height is higher than nominal. More specifically, when the Z height is higher than nominal, the pitch static attitude is more positive than desired and the gram load is lower than desired. All three of these factors cause an increase in the flying height. This problem is further aggravated if the pitch static attitude is higher than nominal when measured at a nominal Z-height and/or the gram load is lower than nominal when measured at the nominal Z-height.
Accordingly, one way of attempting to achieve the desired flying height includes closely controlling the Z-height. Typically, the Z-height of a disk drive depends on the stack-up of many tolerances, including but not limited to the position of the pivot relative to the base, the pivot height relative to the base, and the thickness and flatness of the actuator arm. Typically, the height of the storage disk relative to the base is very precise. Thus, the Z-height can be controlled by closely controlling the individual dimensions and tolerances that determine the Z-height. In other words, tolerances can be tightened so that the actuator arm is brought to the proper Z-height relative to the disk. However, tightening tolerances increases the cost of manufacturing.
Still another way to achieve the desired flying height includes controlling and adjusting the gram load, the pitch static attitude and the roll static attitude. For example, a laser can be used to adjust the pitch static attitude, the roll static attitude and the gram load after the head suspension assembly has been merged into the storage disks. In this design, a harmonic ratio flying height detector is used to estimate the flying height by writing a signal on the disk having a read back spectrum that is constant along the track and which has nonzero amplitude for at least two different frequencies. If the flying height is estimated to be too high or too low, the laser directs one or more laser beams at the load beam to adjust the pitch static attitude, the roll static attitude and/or the gram load. Subsequently, the harmonic ratio flying height detector is again used to estimate the flying height. If the flying height is again too high or too low, the laser again directs one or more laser beams at the load beam to adjust the pitch static attitude, the roll static attitude and/or the gram load. This process is repeated until the desired flying height is determined by the harmonic ratio flying height detector.
Unfortunately, this process is not very practical because the harmonic ratio flying height detector is not very accurate at measuring the flying height and access to load beams that are merged between the storage disks is extremely limited.
In light of the above, the need exists to provide a way to narrow the distribution of the flying heights, the Z-heights, the gram loads, the pitch static attitudes and the roll static attitudes in a population of disk drives. Another need exists to provide a disk drive with reduced track misregistration. Yet another need exists to provide a disk drive that is relatively easy and cost effective to manufacture.
The present invention is directed to a disk drive that includes a drive housing, an actuator arm mounted to the drive housing, a head suspension assembly secured to the actuator arm, a spindle secured to the drive housing, a storage disk positioned on the spindle and a spacer positioned on the spindle. The head suspension assembly includes a slider. The actuator arm includes a suspension mounting side and the spindle includes a disk mounting surface. The spacer is positioned between the disk mounting surface and the storage disk.
With the present invention, a measurement is taken after the actuator arm has been secured to the drive housing. The measurement relates to an actual Z height of the disk drive. As a result of the measurement, an adjustment is made that influences flying height. For example, an actual measured distance along a first axis between the suspension mounting side and the disk mounting surface is measured and the spacer has a spacer height along the first axis that is based upon the actual measured distance. The disk drive has a desired Z height between the suspension mounting side and the storage disk that provides for a good flying height between the slider and the storage disk. With the present design, the spacer height is selected so that the actual Z height is very close to the desired Z height.
In one embodiment of the present invention, the spacer is selected from a group that includes a first spacer having a first spacer height and a second spacer having a second spacer height that is different from the first spacer height. In this embodiment, the first spacer is positioned on the spindle if the first spacer height is closer than the second spacer height to the actual measured distance plus the desired Z height and the second spacer is positioned on the spindle if the second spacer height is closer than the first spacer height to the actual measured distance plus the desired Z height. Stated another way, if the actual distance is equal to X1, the first spacer is positioned on the spindle and if the actual distance is equal to X2, the second spacer is positioned on the spindle.
Further, with the head suspension assembly secured to the drive housing, the gram load, the pitch static attitude, and/or the roll static attitude can be directly measured and adjusted at the actual Z height of the disk drive.
The present invention also includes a method for manufacturing a disk drive. The method includes the steps of providing a drive housing, securing a spindle to the drive housing, the spindle having a disk mounting surface, securing an actuator arm to the drive housing, the actuator arm having a suspension mounting side, and measuring to determine the positions along a first axis between the suspension mounting side and the disk mounting surface.